Bentonite Mixtures Research Articles

Gas transport parameters of differently compacted granulated bentonite mixtures (GBMs) under air-dried conditions

Granulated bentonite mixtures (GBMs) have been regarded as effective buffer materials in the deep geological disposal of radioactive waste due to their operational advantages, such as ease of transportation and in-situ placement/backfilling. Many studies have been done to characterize the hydraulic and thermal properties of GBMs as well as their swelling properties. Only limited studies, however, have investigated their gas transport properties, even though these properties affect their compactness during in-situ placement/backfilling and subsequent gas diffusion and advection in the buffer zone. The aim of this study is to understand the gas transport parameters, i.e., air permeability (ka) and gas diffusivity (Dp/Do), of tested samples compacted at different dry densities (DDs) under air-dried conditions, linking them with the measured density distribution characteristics determined by microfocus X-ray computed tomography (MFXCT) analysis. Two types of GBMs were used in this study: 1) FE-GBM (prepared from National Standard® bentonite, Wyoming, USA): this material was used in the Full-scale Emplacement (FE) experiment at the Mont Terri rock laboratory, Switzerland) and 2) OK-GBM (prepared from a bentonite, originating from Japan, with the trade name of OK bentonite, Kunimine Industries). The tested samples were firstly packed in a 100-cm3 acrylic core with different DDs, ranging from loose to dense (1.09 to 1.75 g/cm3), and scanned by MFXCT. The weighting factors, wf (fine fraction; lower density) and wc (coarse fraction; higher density) (wf + wc = 1), were determined after the peak separation of the measured CT brightness histograms from the reconstructed three-dimensional multiplanar reconstruction (MPR) images of the MFXCT analysis. The measured ka and Dp/Do were highly dependent on the DDs, the ka (ɛ) values fitted well with a power law model, and the Dp/Do (ɛ) was predicted accurately by several previously proposed models. For both FE-GBM and OK-GBM, there were good linear relationships between the gas transport parameters and wc × DD, implying that the weight of the coarse fraction controlled ka and Dp/Do. Moreover, the Kozeny-Carman model, incorporating the measured volumetric surfaces from the MFXCT analysis, was able to predict the ka values well.

Hydro-mechanical behaviour of a cement–bentonite mixture along evaporation and water-uptake controlled paths

The results of a laboratory investigation on the effects of drying and wetting on the hydro-mechanical behaviour of a cement–bentonite mixture are presented. A large hysteresis along the hydraulic paths was found for what concerns both the water retention and the volume strains. This might be related to the shrinkage of cement bentonite clusters and to the development of micro-cracks, that were observed with a microscope along drying. Macroscopic cracks developed in a squat sample which had been cured for 28 days and was then left to dry in the laboratory environment, while this did not occur in an analogous sample cured for 60 days, possibly in virtue of its higher strength as detected through a pocket penetrometer. Water uptake after partial desaturation of squat and column samples took place in short times with respect to drying, but it did not allow for a full recovery of the initial water content. Electrical Resistivity Tomography (ERT) monitoring provided reliable water content determinations in the high range and correct indication of crack patterns at low water contents. A good reproduction of the experimental results was obtained with a coupled Thermo-Hydraulic model formulated on purpose.

Optimization of Sand-Bentonite Mixture for the Stable Engineered Barriers using Desirability Optimization Methodology: A Macro-Micro-Evaluation

In this paper, Desirability Optimization Methodology (DOM) is employed to achieve optimum sand bentonite mixture (SBM) based on multiple antagonist macro-geotechnical responses of the compacted SBM prepared using poorly graded sand with the mean grain size around 0.2 mm and bentonite with plasticity index around 157% for the stable engineered barriers (EBs). For this purpose, varying mix designs of SBM compacted at compaction energy of 2,700 kN-m/m3 are initially tested to determine their mechanical properties, volumetric-change behavior, and hydraulic conductivity. The unconfined compressive strength, cohesion, angle of internal fiction, swell pressure, compression index, and hydraulic conductivity are taken as the geotechnical design parameters for the SBM. Mathematical models are developed and statistically validated for these design parameters using sand content (SC) and bentonite content (BC) as the predictors. In addition, models are also developed to predict compression curves for compacted SBMs. Moreover, microstructural evaluation is conducted through scanning electron microscope (SEM) analysis to determine the SBM having a desirable microstructure for stable EB. It is observed that a major shift in the microstructure from medium pores to micro-pores occurs for the BC between 20% and 30%. Afterward, optimization of SBM is carried out by integrating developed models for the geotechnical design parameters in a desirability function (D) algorithm, which is subsequently simulated by setting maximization of strength and minimization of swell pressure, compressibility and hydraulic conductivity of compacted SBM as the goals. A reasonably high D-value is achieved for the SBMs having SC:BC in a range of 74:26 to 78:22 with the highest at 75.63:24.37 against the set goals. This study manifests an effective and pragmatic strategy for designing the SBM for a stable EB considering its antagonist hydraulic, volumetric change, and mechanical responses.

Effects of microplastics on evaporation dynamics in porous media

Microplastics (MPs) pollution is an emerging threat to soil ecosystems. The present study aims to investigate the impacts of MPs on soil water evaporation dynamics and patterns. Two series of laboratory experiments were conducted using sand particles and clay mixed with different MPs to investigate how evaporation dynamics and patterns are influenced by the presence of MPs. Quartz sand including 0, 0.75, 1.5, and 4.5% of Polyethylene (PE) and Polyvinylchloride (PVC) were used to evaluate MPs effects on evaporation rates while bentonite mixed with sand and 0, 0.75, 1.5, 4.5, 6, 8, and 10% of PE and PVC were used to investigate evaporation-induced cracking patterns. The experiments were conducted under controlled laboratory conditions in a climate chamber at constant ambient temperature. Our results suggest that the addition of MPs led to more water evaporation compared to the samples without MPs. Microscopic imaging and analysis enabled us to evaluate the possible MPs effects on the modification of soil characteristics and pore structure affecting the evaporation behavior. Moreover, although increasing MPs concentrations appeared to induce only minor effects on the crack morphology formed as a result of evaporation from the mixture of sand and bentonite, the type of MPs (PE vs PVC) had more notable effects on the drying-induced cracking patterns. The reported experimental data and analysis extend our physical understanding of the parameters influencing soil water evaporation in the presence of MPs.

Membrane Behavior of Kaolin–Bentonite Mixtures

Membrane Behavior of Kaolin–Bentonite Mixtures

Improvement of Shear Strength of Zeolite-Bentonite Liner Material under High Temperatures with Tincal and Pumice

Thermal changes (high temperature and thermal cycles) occur around energy structures, such as energy piles, nuclear waste repositories, etc. Sometimes these temperature changes affect the engineering properties of surrounding soils undesirably. Hence, there is a need for durable soils that can maintain their engineering properties unchanged under high temperature and thermal cycles for a long time. Tincal and pumice are used in the production of temperature-resistant and heat-insulated materials. Therefore, in the present study, 10% and 20% tincal and pumice additives were added to zeolite-bentonite mixtures and shear strength behavior of the mixtures was investigated under room and high temperatures (80°C). According to the results, the maximum shear stress values of zeolite- bentonite mixtures generally increased in the presence of tincal and pumice additives under high temperature. Both additives are effective for improvement, however; the effect of pumice can be more pronounced.

Development, Synthesis and Characterization of Tannin/Bentonite-Derived Biochar for Water and Wastewater Treatment from Methylene Blue

Novel hybrid carbon–mineral materials were synthesized by the mechanochemical activation of a mixture of tannin and bentonite in a ball mill with further pyrolysis in an argon atmosphere at 800 °C. The influence of the initial mixture ingredients content on the structural, textural, and thermal characteristics of biochars has been described using X-ray diffraction, Raman and Fourier-transform infrared spectroscopy, nitrogen adsorption–desorption, and scanning electron microscopy. The influence of bentonite clay on the carbon phase characteristics due to the formation of more heat-resistant and structured nanocarbon particles in biochars has been proven. The adsorption effectiveness of the materials towards methylene blue was studied. The adsorption data were analyzed applying Langmuir and Freundlich isotherms with high determination coefficients (R2) in the range of 0.983–0.999 (Langmuir) and 0.783–0.957 (Freundlich). The maximum adsorption amount of MB was 5.78 mg/g. The adsorption efficiency of biochars with respect to phenol was also examined. It was shown that the hybrid biochars show differentiated selectivity to the adsorption of organic compounds. It was concluded that the physicochemical properties of the surface of biochars play an important role in the adsorption effectiveness, making them a good candidate for water and wastewater remediation processes.

Hydraulic conductivity of compacted manufactured sand tailings–bentonite mixtures: a new hydraulic barrier material

Hydraulic conductivity of compacted manufactured sand tailings–bentonite mixtures: a new hydraulic barrier material

Co-pyrolysis of wood chips and bentonite/kaolin: Influence of temperatures and minerals on characteristics and carbon sequestration potential of biochar

Biochars have been highlighted as a means of carbon sequestration, which is significant for achieving carbon neutrality. Mixtures of wood chips and either bentonite or kaolin were co-pyrolysed at temperatures of 350 °C and 550 °C, and the microstructural characteristics and the carbon sequestration potential of the resultant biochar were explored in the study. The addition of minerals promoted the formation of a stable carbon structure in biochar, especially the proportion of SiC bonds in the high-temperature mineral-composited biochar increased by 3.56–3.82 times compared with the original biochar. After bentonite or kaolin was added to wood chips pyrolysed at 550 °C, the carbon loss after H2O2 oxidation was reduced to no more than 19.2%, and the Recalcitrance Index (R50) of biochar increased to no less than 0.89. The combined action of high temperature and minerals promoted the formation of highly aromatic structures of biochar (H:C < 0.4) and reduced the amount of dissolved organic carbon to 4.89 mg g−1. Furthermore, minerals directly covered the surface of biochar, and the content of SiC bond increased, thus strengthening the chemical and thermal stability of biochar. However, the addition of minerals had no significant effect on the biological stability of biochar. The study indicates that the pre-pyrolysis mineral addition is an effective way to increase the carbon sequestration potential of biochar.

Saturated hydraulic conductivity of compacted steel slag-bentonite mixtures——A potential hydraulic barrier material of landfill cover

The feasibility of using steel slag and bentonite mixtures to construct the hydraulic barrier of a landfill cover was explored in the present study. Fine-grained steel slag (SS; particle diameter < 1 mm) and sodium-activated calcium bentonite (SACB) were used to prepare compacted specimens, and the saturated hydraulic conductivity (ks) was measured using a flexible-wall permeameter. Influential factors including SACB content (BC), SS gradation, water-washing treatment of SS and compaction water content (ωcomp) were investigated. The hydraulic conductivity results were interpreted in microscopic scale through mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). It was found that when BC was below 10%, the ks value of the specimens prepared with well graded SS was about one order of magnitude lower than that of the specimens prepared with poorly graded SS. This was due to less macropores caused by better SS gradation. Yet, the effects of SS gradation on ks diminished as BC further increased to 15%, suggesting the dominant role of BC on ks at high BC. Water-washing treatment of SS helped reduce ks significantly to 1.2 × 10−10 m/s at BC of 10%, owing to less multivalent cations and hence lower osmotic swelling reduction caused by cations. Controlling ωcomp 1–2% wetter than the optimum water content (ωopt) also helped reduce ks significantly, owing to the reduction of macropores. Accordingly, it is suggested to use well-graded SS mixed with 10% SACB and then compact at ωcomp slightly wetter than ωopt to the degree of compaction greater than 90% in engineering practice.

Investigation of the emplacement dry density of granulated bentonite mixtures using dielectric, mass-balance and actively heated fiber-optic distributed temperature sensing methods

Granulated bentonite mixture (GBM) is considered to be one of the key elements of the engineered barrier system in the Swiss concept for disposal of spent fuel/vitrified high-level waste. To demonstrate the full-scale emplacement of GBM using a prototype backfilling machine consisting of five screw feeders, an 8-m-long mock-up tunnel in a warehouse and a 50-m-long tunnel in the Mont Terri rock laboratory were backfilled. To ensure the successful emplacement of the GBM in these tests, attempts were made to quantify the dry density of the GBM using conventional mass-balance averaging as well as tools based on dielectric and heated fiber-optic methods. In the mock-up test, the dry density was measured using a set of dielectric tools installed through the tunnel wall. Heterogeneity over the tunnel cross-section was captured, with a general trend towards higher dry density near the screw feeders and lower values near the tunnel wall and crown areas. The in-situ tunnel backfilling in the Mont Terri rock laboratory was performed in twelve steps and the section-wise average dry densities along the tunnel showed a longitudinal variation. Nonetheless, both mock-up and in-situ backfilling tests showed that the overall average dry density exceeded the target value of 1,450 kg/m3. The fiber-optic method involved actively heating the fiber-optic cable installed near the GBM-shotcrete interface at the crown of the tunnel. The GBM dry density profile along the cable was estimated based on the temperature responses. The estimated dry density near the tunnel crown indicated longitudinal variations and was generally lower, which was consistent with the results of the mock-up test. The three methods provided the GBM dry density at different locations with different spatial resolutions. However, the combined results demonstrated that GBM backfilling met engineering and safety-relevant requirements.

Water/Cement/Bentonite Ratio Selection Method for Artificial Groundwater Barriers Made of Cutoff Walls

As urban development requires groundwater table isolation of various historically polluted sources, the necessity of building effective, strong, flexible, and low-permeability cutoff walls raises the question of choosing optimum construction materials. Various authors have proposed water–cement–bentonite mixtures, which are often chosen by experience or a trial-and-error approach, using classical methods for testing (Marsh funnel) and representation of results (water–cement ratio, water–bentonite ratio). The paper proposes a more precise approach for assessing the viscosity and global representation of the three components. Moreover, this approached is exemplified with a better documented recipe for the choice of materials based on laboratory results. The representation of the mixtures was undertaken on a limited domain of a ternary diagram, where the components are given in terms of mass percentage. The derived properties (viscosity, permeability, and compressive strength) are presented on a grid corresponding to the physically possible mixtures. Based on this representation, the most efficient recipes are chosen. Because the mixture contains only fine aggregates, the viscosity was determined using a laboratory viscosimeter.

Methanol to Gasoline (MTG): Preparation, Characterization and Testing of HZSM-5 Zeolite-Based Catalysts to Be Used in a Fluidized Bed Reactor

The preparation of catalysts suitable for MTG processes in a fluidized bed reactor has been studied with emphasis on improving the textural, physico-chemical, morphological, structural and mechanical properties. A mixture of HZSM-5 zeolite (active material), boehmite or bentonite (binder) and alumina (inert filler) was used to prepare different catalysts. After preparation, characterization by physical adsorption of N2, XRF, XRD and SEM-EDX techniques was carried out. The screening of catalysts was performed in a fluidized bed reactor. The distribution of products was very similar in all cases, with the yield of light hydrocarbons always being higher than that of gasoline. Among the catalysts tested, the one containing boehmite as a binder (HZ_Boeh) was found as the most appropriate due to its high mechanical strength, high yield to aromatics and lower yield to durene.

Contaminant migration and the retention behavior of a laterite–bentonite mixture engineered barrier in a landfill

Groundwater pollution has become increasingly severe in recent years, particularly owing to leachate leakage in landfills. In this study, the migration of Cu2+ in a landfill and the retention behavior of a compacted laterite-bentonite engineered barrier system toward the contaminant were analyzed by a numerical simulation based on laboratory and field test results. The results show that the hydraulic conductivity of the laterite–bentonite mixture decreased with an increase in the bentonite ratio: The hydraulic conductivities of the laterite–bentonite mixture were 4.718 × 10−7, 2.103 × 10−7, 7.899 × 10−8, 3.918 × 10−8, and 1.614 × 10−8 cm/s when the bentonite ratios were 0, 2%, 5%, 10%, and 20%, respectively. The hydraulic conductivity of laterite and of the mixture with a bentonite ratio of 2% decreased gradually under infiltration of deionized water and CuSO4 solutions with concentrations of 0.01 and 0.1 mol/L. This could be attributed to the increased degree of flocculation of laterite with the increase in the solution concentration. The results of the numerical simulation indicate that the migration range of Cu2+ after 3650 days was approximately 1500 m. The retention efficiency of a 0.5 m engineered barrier for Cu2+ was 67%. However, the retention efficiency exceeded 83% when the engineered barrier thickness was increased to 1.0 m. The results of the laboratory tests and numerical simulation demonstrate that a compacted laterite–bentonite engineered barrier system has a good retention effect on Cu2+. These observations may provide effective concepts for the prevention and control of groundwater pollution in landfills.

Effect of Bentonite Content and Hydration Time on Mechanical Properties of Sand–Bentonite Mixture

The bentonite is commonly used mixed with soils for groundwater retention and waste contaminant facilities. The incorporation of bentonite could significantly reduce hydraulic conductivity. In this study, the effects of bentonite content, hydration time and effective confining pressure on the static properties of a sand–bentonite mixture were studied using experimental and numerical methods. Firstly, a large number of drainage static triaxial tests on the sand–bentonite mixture with various bentonite contents were conducted. The test results show that the increase in bentonite content and hydration time leads to a slight decrease in shear strength and initial tangent modulus of the sand–bentonite mixture. The presence of bentonite reduces the shear shrinkage and dilatancy trend of the mixture. The cohesion of the mixture increases with the increase in bentonite content and hydration time, but the internal friction angle decreases correspondingly. The hydration of bentonite on the surface of sand particles changes the contact form between particles. The bentonite slurry between pores of the sand skeleton also affects the mechanical behavior of the sand–bentonite mixture. Then, a series of 3D discrete element models were established for numerical simulations of drainage static triaxial tests. The numerical model parameters were calibrated by experimental results. The meso-mechanism of bentonite content affecting the mechanical behavior was revealed according to the contact force distribution between particles. The research results are helpful to understand further the mechanism of bentonite on the mechanical properties of the sand–bentonite mixture.

The Use of Natural Sorbents to Reduce Ammonia Emissions from Cattle Faeces

Intensification of animal production leads to an increase in ammonia emissions into the environment. For this reason, various methods and strategies are sought to reduce ammonia emissions from faeces. The aim of the study was to test the possibility of using natural sorbents and sorbent mixtures to reduce ammonia emissions from cattle faeces. Faecal samples for analysis were collected from Holstein-Friesian dairy cows during the winter. The amount of ammonia emissions from cow faeces was determined every seven days, after mixing the faeces with a mixture of selected sorbents. All of the sorbents used have the potential to remove ammonia. The most effective reduction in ammonia was achieved using biochar and a mixture of bentonite with zeolite. The reduction in these groups was 42.56% and 24.56%, respectively, relative to the control group. The results indicate that these sorbents can be used to reduce ammonia emissions from cattle farms.

Improvement of thermally durable soil material with perlite additive

Thermal changes affect the engineering behavior of surrounding soils at energy geostructures. For that reason, there is a need for durable soils which are not affected from high temperatures or thermal cycles. Such soil mixtures can be developed by adding temperature-resistant materials such as perlite to the sand–bentonite mixtures. In this study, 10 and 20% perlite additives were added to 10 and 20% sand–bentonite mixtures, in order to develop durable soil mixture under high temperatures. Direct shear and hydraulic conductivity tests were performed under room temperature and high temperatures. The results of the experiments showed that the perlite additive reduced the dry unit weight of the sand–bentonite mixtures and had a positive effect on the shear strength of 20B–80S mixtures both under room and high temperatures. The perlite addition increased the angle of internal friction of sand–bentonite mixtures under room and high temperatures especially for 20% bentonite–80% sand (20B–80S) mixtures. The hydraulic conductivity (k) values of both mixtures increased with increasing temperature. As a results of thermal cycles, it was seen that the samples cannot turn back to their initial k values.

Recycled waste tire fiber as a sustainable reinforcement in compacted sand–bentonite mixture for landfill application

A layer of compacted sand-bentonite (CSB) mixture is employed as a liner at the landfill. The formation of desiccation-induced shrinkage cracks can increase the leachate migration into groundwater. The usefulness of the liner system may be endangered if the liner material's strength is insufficient. To address this issue, the CSB barrier can be modified by incorporating with waste tire fiber. This study aimed to assess the undrained shear strength, consolidation, and desiccation-induced crack of mixtures of CSB and reinforced CSB. An analytical model was derived to assess the behaviour of tire fiber composite soil from the experimental result. Positive excess pore water pressure was reduced significantly by the inclusion of tire fiber in the consolidated undrained triaxial test results. By the addition of 15% tire fiber, the effective frictional angle was raised from 21.0° to 24.2°, while the effective cohesion component was increased from 15.0 kPa to 24.2 kPa at the same fiber content. The crack density factor and crack intensity factor of the mixture without tire fiber were much higher than those of the CSB with fiber. By the addition of tire fiber, time for 90% consolidation was reduced, while the coefficient of consolidation increased. Although the permeability increased marginally, but it was within the limiting value. An analytical model adequately captured the stress-strain and pore water pressure responses of all proportion of tire fiber, and the yield surface of the composite was expanded maximally with only 10% tire fiber.

Effect on engineering properties of ground granulated blast furnace slag admixed with laterite soil, cement and bentonite mixtures as a liner in landfill

This paper showcases the geotechnical and environmental engineering properties of ground granulated blast furnace slag (GGBS, a byproduct of iron-ore) admixed with local laterite soil (LS), bentonite (BT) and cement (CT) mixtures as landfill liner. The main aim of this study is to determine the effect of GGBS on LS (i.e. effect of binder material with filler material) and to study the effect of GGBS-LS blended with varied BT and CT mixtures (i.e. binder-filler material in partial replacements), to perpetrate as a landfill liner material. Overall, a wide range of fifteen unique mix proportions was chosen in this study and are categorized into five series. Laboratory tests such as consistency limits, free swell index (FSI), Proctor compaction, hydraulic conductivity (HC), leachate characteristics (LC) and unconfined compressive strength (UCS) with post-testing analysis were conducted to evaluate the optimum mix. From the test results, the consistency limits and FSI decreased with an increase in GGBS content for all the mixes. In compaction tests, the addition of GGBS increases the dry unit weights and reduces the water contents. The HC decreased with the addition of GGBS quantities when permeated with deionized water and diesel oil as permeant fluids. In the LC, the concentrations of heavy metals (i.e. Cr, Co, Cd, Fe and Pb) in diesel oil decreased and removal efficiencies increased for lower HC values than higher HC values. The UCS values increased with an increase in GGBS quantities and curing intervals for all the mixes. The microstructure and mineralogical analysis revealed the identification and confirmation of new cementitious products which ameliorated the UCS values. Hence, from this study, when GGBS admixed with filler and other binder material established to be an efficacious and eco-friendly solution which not only reduces the disposal problem but improves the engineering properties and prerequisite as landfill liner.

Stability performance of demolition waste composite as landfill liner

Landfill liner is one of the essential components that prevent leachate infiltration of the soil from causing pollution. A liner has specific design criteria to function optimally. This study analyses the permeability and stability value of the mixture of composite materials consisting of demolition waste, bentonite, and lime materials. This study using some methods include falling head method for permeability test and direct shear strength for stability test. Based on the results of this research, it can be seen that the mixture of demolition waste and bentonite to composite can reduce the internal shear angle and increase the cohesion. While lime provides a fluctuating value for cohesiveness, it can increase the internal shear angle. The best mixture to be used as an alternative composite liner is the V6 composite which has a demolition waste composition of 79%, 20% bentonite, and 1% lime with a permeability coefficient value of 8.526 × 10−7 cm/s.